Liquid crystal display apparatuses for image display are widely used as large-sized displays of flat-screen televisions and monitors, etc. These liquid crystal display apparatuses employ a backlight unit that applies illuminating light to a liquid crystal display panel from the back or the lower side of the liquid crystal display panel to enhance the luminance of the display screen.
The above-described backlight unit has a lightguide plate and a light-emitting diode (LED) light source disposed at a peripheral side surface of the lightguide plate. The lightguide plate guides light from the light source through the lightguide plate and emits the guided light from the whole area of a light-exiting surface of the lightguide plate toward a liquid crystal display panel that faces the lightguide plate.
Recently, as liquid crystal televisions increase in size, there has been a demand for further reduction in weight and thickness of backlight units used in the liquid crystal televisions. In this regard, as the thickness of lightguide plates in backlight unit is reduced, it becomes more likely that color irregularity and luminance unevenness will occur on the light-exiting surface of the lightguide plate. If injection molding is employed as a method of producing a large-sized lightguide plate, it is difficult to fill the resin material throughout the molding tool for the large lightguide plate. This problem can be solved by increasing the injection pressure. This, however, causes an increase in cost of equipment.
Meanwhile, there has been developed a planar light-emitting device in which a plurality of lightguide plates having respective light sources are arranged in a matrix with their respective light-exiting surfaces being flush with each other to obtain a wide light-exiting surface as a whole (see Japanese Patent Application Publication No. Hei 11-288611).
The above-described conventional planar light-emitting device, however, still has the following problems to be solved.
The light sources of the lightguide plates arrayed in a matrix are all arranged to emit light in the same direction. Therefore, the pattern of highs and lows in the luminance distribution on one lightguide plate matches that on another plate adjacent to it. These highs-lows patterns affect each other to aggravate the luminance unevenness, resulting in an uneven overall distribution of luminance on the light-exiting surface of the planar light-emitting device. When lightguide plates are regularly arranged in a matrix, the vertical and horizontal joints between four mutually adjacent lightguide plates intersect each other in a cross shape, and the center of the cross-shaped intersection is likely to become a dark spot because a sufficient amount of light cannot reach there.